Factors And Mechnisms Inducing Necrose Lesions On Bagged Apple Fruit And Fiungicides Screening

Spot disease was an important disease of bagged apples since 2000 when apple bagging cultivation was widely impled, resulting in 3% to 30% yeald loss every year. The infection process and pathogenic mechanism of pathogen are still not clear, which limited the understanding to the disease occurance, epidemic characteristecs and control technicians resulted in that the disease can not be controlled efficiently. In recent years, this disease was increasing year by year. In order to get further insight into the pathogenic menchanisms of Trichothecium roseum and effective germicides, we have studied the effects of fruit bagging to the community structure of fungi in cuticle and core of apple fruit, fruit character and nutrients absorption of fruit; the effects of temperature and relative humidity on conidium germination, infection, survival and sporulation of Trichothecium roseum; the bagged fruit were inoculated verification on order to clear the infection date of pathogen; cleared the pathogen infection orifice in fruit by observing of scanning electron microscope; tested control effects of several fungicides on Trichothecium roseum. Results were showen as follows.Three ordinary orchard, one was in Hai-yang in 2011 and the others were in Peng-lai and Qi-xia in 2013, were chose to isolate fungi from bagging fruit and un-bagging fruit with traditional tissue isolation. The isolated fungi were identified according to morphology and ITS sequences. Species richness, colony number, colonized ratio, diversity index, coefficient of similarity and isolation frequency of fungi isolated from four units, i.e. cuticles of bagging fruit, core of bagging fruit, cuticles of un-bagging fruit and core of bagging fruit were calculated and analyzed. The result showed that, In the two years,43 and 31 genera of fungus were isolated from cuticle and core of apple fruit respectively. Alternaria spp., Cladosporium cladosporioides, Fusarium spp. and Penicllium spp. were the fungi which were isolated with higher frequencies. Species richness and diversity index of fungus colonized on cuticles was decreased while tissue colonized ratio and colony number was increased with the fruit bagging. Coefficient of similarity of fungus species richness colonized on cuticles of bagged and un-bagged fruit decreased gradually with growing of apple. Species richness of fungus colonized on bagged fruit cuticles was significantly decreased at July and August. Few fungi, such as Alternaria spp., grow to the dominant fungi on cuticle of bagged fruit at the end of August. Species richness and colony number of fungus colonized in the core of fruit maintain a stable level in long terms after fruit bagging. Coefficient of similarity of fungus species richness colonized in the core of bagged and un-bagged fruit decreased with an unobvious variation. There was no significant difference in species richness and colony number of fungus seprated from the core of fruit between the end of May and September. Fungus infected the core of fruit dominate at flowering and young fruit period.System monitoring results of two years showed that, apple-bagged can promote the growth of fruit, increase the diameter and weight of apple fruit and promote the fruit pulp cell division at early stage. With the growth of the fruit, Stomas grew into lenticels gradually. The number of stomas grew into lenticels was more than 85% in June and July. Apple-bagged has no significant effect on the transformation of stomas to lenticels and the growth of lenticel. N, P and Ca elements content showed a gradual decline trend with the growth of fruit. There was the fastest reduce speed in June and July. K and B elements content remained relatively stable throughout the fruit growth period. Apple-bagged has no significant effect on the content and change of elements. The temperature inside the bag was significantly different with the temperature outside the bag after fruit bagging. The temperature inside the bag was 0.61℃ higher than that outside the bag. The temperature difference between inside and outside the bag was maximum at 8:00 and the average temperature difference was 1.75℃, followed by with 14:00 and the average temperature difference was 1.1 ℃. There was no significant difference on the average relative humidity between inside and outside the bag. The average relative humidity outside the bag was 5.7% higher than that inside the bag and they had a significant difference.The temperature range for c conidia is between 15 and 35℃ and optimum temperature is 30℃. High humidity above 95% and free water is essential for germination of conidia. The germination rate in high humidity is higher than that in free water. There was a great influence of temperature to the survival time of conidium under the condition of moisture. Conidium are still alive after 16 days under 20 ℃ while conidium almost all died after 6 days under 30℃.The complex microelement such as vitamin inside Bark, fruits, flowers can promote conidium germination of Trichothecium roseum. Fruit calyx residual withered petals, stamens, pistil and stigma provided rich nutrients for the colonization, spore production, germination and infection of Trichothecium roseum. Rainfall is the necessary condition pathogen infecting bagged fruit During the growth of apple fruit.The results of the inoculation with spore suspension and Chinese flowering crabapple at different times in 2014 showed that the pathogen Trichothecium roseum caused "black spot type" lesions. Generally the incidence of spot disease higher before early July and after July dropped. The incidence of spot disease was the most highest in the Mid-july because which temperature and relative humidity were the biggest in the whole growing season, which suggested that the early stage of fruit was sensitive to spot disease.In order to screen effective fungicides to control apples pot disease caused by Trichothecium roseum, control efficiency and the treatment effect of 10 fungicides and effective duration of 5 fungicides were tested by applying the fungicides before inoculating and inoculating before applying the fungicides. The rusults showed that control efficiency to control Trichothecium roseum of three fungicides, mancozeb, thiophanate-methyl, carbendazim were 100% and the effective duration would maintain 40 days. The treatment effect of mancozeb, thiophanate-methyl were 100%, which had good therapeutic effect.